Polyolefin blends are well known. Films from polyolefin blends are known, but because property requirements vary with different applications and because film properties such as tear strength are based upon tradeoffs between processing, thickness, and modulus, further improvements are needed. U.S. Pat. No. 6,649,698 discloses blends of high molecular weight HDPE with LLDPE and their improved environmental stress crack resistance. The blends are used as geomembranes (polymer sheets used as environmental barriers) and pipes. Environmental stress crack data is given, but there are no other reported properties of the blends. There is nothing disclosed about thick films. There is no indication of improved tear strength.
Thin films have been studied for applications such as grocery sacks. U.S. Pat. No. 4,346,834 improves the thin film (preferably between 20 and 40 microns) properties of LDPE by blending 5-20% by weight HDPE and LLDPE with the LDPE to provide a ternary blend. All of the blends contain LDPE and there is nothing disclosed about thick films.
U.S. Pat. No. 6,355,733 discloses a blend of LLDPE with medium density polyethylene having multimodal molecular weight distribution. The reported blends have a low modulus (examples range from 52,000 to 62,000 psi) and a low density (examples range from 0.927 to 0.931 g/cm3). The disclosure states that HDPE blends with LLDPE do not usually perform synergistically and solves this problem by using MDPE with multimodal distribution.
Despite the considerable amount of work done with polyolefin blends, apparently thick films with high machine direction tear strength, density from 0.935 to 0.955 g/cm3, and modulus from about 75,000 psi to about 130,000 psi have not been prepared from HDPE and LLDPE blends.